1. Field of the Invention
The present invention relates to a key switch structure of a keyboard that is used as an input device in an information processing device, a measurement instrument, or a medical instrument, and in particular relates to a key switch structure including a lighting function that can ensure good operability even in a dark environment.
2. Description of the Related Art
Conventionally, the development of keyboard devices that can ensure good operability even in a dark environment has been carried out. For example, there is a keyboard device of the structure shown in FIG. 17. To describe this keyboard device using FIG. 17, a character or symbol is printed on the upper surface of a key top 1, an elastic member 2 and a link mechanism 3 are disposed below the key top 1, and a membrane sheet 5 and a reinforcement plate 6 including a contact portion 4 are disposed below the elastic member 2 and the link mechanism 3. An EL light emitting portion 7 is disposed on the upper portion of the membrane sheet 5.
The EL light emitting portion 7 is formed by printing on a dedicated sheet 8, and light is emitted from the underside of the key top 1 by the EL light emitting portion 7. As a result of light being emitted from the underside of the key top 1, the character or symbol printed on the key top 1 is brightly lighted and can be seen. Examples of publications that disclose a key switch that uses an EL element to light the key top 1 include Japanese Patent Application Publication (JP-A) No. 2002-251937.
However, in the above-described conventional keyboard device of the key switch structure using an EL element, it is common for the lighting lifespan of the EL element to be about 3,000 hours, which is relatively short, and there has been the problem that the key switch structure cannot be employed in an information processing device, a measurement instrument, or a medical instrument whose use for several years is to be assured. Moreover, there has also been the problem that the product becomes expensive because an inverter that supplies high-frequency/high-voltage alternating current in order to cause the EL element to emit light is necessary.
Further, when an EL element is disposed in a keyboard including a link mechanism portion widely employed in personal computers, it is difficult to dispose the EL element directly below the link mechanism portion disposed on the underside of the keyboard, and there is no choice but to dispose the EL element in a place other than directly below the link mechanism portion. For that reason, there has also been the problem that it is difficult to obtain lighting of the keyboard that is uniform and good.